This invention relates to a method of stabilizing gravel, sand, crushed stone, rock and concrete structures which are cracked, porous or have other cavities difficult of access, and sealing the same against flows of water by injecting a pumpable, low-viscous aerated concrete which is based on an aqueous dispersion containing finely-ground cement, a dispersing agent and optionally fine-particulate material having a large specific surface.
When stabilizing and sealing gravel, sand, rock and concrete structures, which are porous or cracked, or have other cavities difficult of access, it is generally known to inject pumpable, easy-flow concrete containing cement and frequently various additives, such as accelerators and retarders controlling the curing of the cement, and fine-particulate material promoting the sealing of the cavities. However, it has been found that in many cases it is difficult to achieve a satisfactory result. For instance, it has proved to be difficult to make the injected concrete reach sufficiently far into the narrow cavities to obtain a satisfactory seal against penetrating water. It has also been found to be difficult, in e.g. rock which conducts great amounts of water, to apply the concrete and make it cure before an increase of the water-cement ratio occurs and the concrete is wholly or partly flushed away.
According to the present invention, it has now been found possible to solve these problems and present an effective method of stabilizing and sealing gravel, sand, crushed stone, rock and concrete structures. The method is characterised by injecting aerated concrete with a pore volume of at least 20% by volume into the cavities that are difficult of access and are to be sealed. The injection should be carried out by first injecting the aerated concrete at such a low pressure that the aerated concrete remains intact, and then applying an increased pressure, such that the air bubbles located in or in the vicinity of the cavity are pressed further into the cavities and collapse, whereby air entrains cement and a fine-particulate material, if any, into the cavities, where sedimentation and hydration take place. The pressure when injecting the aerated concrete is suitably below 3 bar while the increased pressure usually is above 6 bar.
By applying the inventive method, it has been found possible to considerably reinforce the stabilization by the fact that the hydratable concrete mixture can penetrate further into the cracks than is possible when injecting a conventional concrete mixture. The cement is suitably finely ground to such a particle size that at least 95% pass a screen having a mash size or 64 xcexcm, preferably 34 xcexcm and most preferred 16 xcexcm if penetration into fine cavities is desired. The air bubbles and the escape thereof through the cavities also prevent penetration of water during injection and thus prevent, at least partly, the fresh concrete from being diluted with water and make any flushing away difficult. If the flowing through of water is extremely great or if a low water permeability is desired, it has according to the invention been found to be suitable to use hydrophobic aerated concrete. Preferably the aerated concrete is hydrophobised to such an extent that it does not spontaneously mix with water. As a result, dilution of the mixture with water is avoided while at the same time the risk of flushing away is considerably reduced.